This invention relates to a cyclone, particularly for multistage heat exchangers, having an externally arranged inlet spiral and a gas pipe which is fed from below and which is bent at substantially a right angle immediately before the inlet spiral.
Multistage cyclone heat exchangers are used for example as preheaters in cement calcining installations. In an effort to reduce the overall height of multistage cylone preheaters of the type in question, attempts have been made to further reduce the overall volume of the cyclones. However, this has given rise to serious separation problems in view of the high dust content of the gases in heat exchangers of this type.
In order to achieve an acceptable degree of separation, the externally situated inlet spiral should extend over a peripheral angle of at least 180.degree.. However, this necessitates a considerable overall volume and weight of the cyclone. Added to this is the fact that, where several cyclone stages are arranged one behind the other, the gas flow undergoes a substantially right-angled deflection before entering the cyclone which leads to separation of the dust in the gas and results in a particularly heavy accumulation of dust in the uppermost part of the inlet spiral.
Now, if a cyclone of the type in question is made very small and if only a very short dip pipe, if any, is installed on account of the high working temperatures, practical experience has shown that hardly any separation-assisting vortex is developed in the cyclone. Instead, the vortex breaks up after only about half a revolution and the gas flows through the outlet opening to the next cyclone stage. In the lower two thirds of the overall height of the cyclone, there is no significant separation of dust through vortex formation.